1. Field of the Invention
The present invention relates to a fuel control apparatus for an internal combustion engine provided with a fuel vaporized gas diffusion prevention device for preventing diffusion of fuel vaporized gas generated in a fuel supply system of a motor vehicle.
2. Related Art
Until recently, vaporized fuel generated in a fuel tank has been adsorbed by active carbon, which is then purged into an adsorption system. For instance, Japanese Laid-Open Patent Publication No. 289243/1988 discloses performing correction of a fuel injection quantity in addition to performing air-fuel ratio feedback correction in response to an air-fuel ratio of a mixture when the purging is attained. The purge correction quantity is set according to the concentration of vaporized fuel obtained from the average value of the feedback correction coefficient, thereby improving control of the air-fuel ratio.
However, because actual purge quantity varies in dependence on piping conditions of the purge system, the air-fuel ratio control is degraded. For instance, pressure loss is caused in the piping of the purge system. This will result in a decrease of the actual purge quantity from a theoretical purge quantity. Further, an intake conduit and a canister are not disposed next to one another. Instead, they are located apart from each other. Thus, the actual purge quantity is delayed due to pressure loss in a supply conduit or the like. A purge quantity is not increased proportionally after purging starts, but the purge quantity is gradually increased instead. This causes a delay in the actual purge quantity. Accordingly, control of an air-fuel ratio in transition worsens and both emissions and the drivability of the vehicle are influenced. Furthermore, recently, the mounting of a large canister on a rear portion of a vehicle in order to minimize generation of vaporized fuel has been proposed. However vehicles including such a structure have been found to have an adverse effect on the air-fuel ratio.